Do you hire an accountant to do your taxes? Or a financial planner? Is it your job to micromanage those people? Or do you think that when you pay those people money, it's their responsibility to take care of you?

The agent has done his job so long as he explained this obligation to the client before the contract was signed. Assuming that happened, the agent isn't necessarily in wrong here. However, it would be better quality service as an adviser and in their own best interest to make efforts to remind the client about this provision and particularly as it seemed to only be applicable in the final year of the deal.